A pressurizer for a pressurized water nuclear power plant is a pressure vessel that is part of the main primary system of the plant. It is composed of 3 vertical cylindrical shells and two hemispherical caps at the two ends. It is constructed in ferritic steel with a coating in austenitic stainless steel over all inner surfaces in contact with the primary fluid. The pressurizer is equipped, on its lower part, with vertical heaters and a connecting branch with an expansion line. On its upper cap, it comprises a nozzle equipped with a thermal sleeve and a spray head. The thermal sleeve allows the nozzle to be protected against excessive thermal changes, thus reducing as much as possible damage due to fatigue. The nozzle is made of ferritic steel and is covered on its inner face with a stainless steel coating. The nozzle is connected to a spray pipe via a safety end piece in austenitic stainless steel. The weld between the nozzle and the end piece is thus made in the form of a bimetallic weld while the weld between the safety end piece and the spray nozzle in austenitic stainless steel is made by using a homogeneous weld.
In general, document FR0158544 describes a thermal sleeve welded to the inside of the conduit in which it is located. Replacing this sleeve involves cutting the conduit twice before the sleeve can be removed by eliminating the weld bead of the sleeve on the conduit.